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Electromagnetic Wave And Communication Mcq
Quiz 6
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Q.1
A new system of unit is evolved in which the values of µ0 and εo are 2 and 8 respectively. Then the speed of light in this system will be
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a)0.25
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b)0.5
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c)0.75
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d)1
Explanation
Answer: (a)
Q.2
Our eyes respond to wavelength ranging from
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a) 400nm to 700nm
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b) 1mm to 700nm
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c)-∞ to +∞
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d)700nm to 800nm
Explanation
Answer: (a)
Q.3
In microwave oven, we use electromagnetic oscillators which produce electromagneticwaves in the wavelength range
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a) 1mm to 10m
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b) 0.7µmto 1mm
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c)0.1m to 1mm
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d)0.1µmto 0.7µm
Explanation
Answer:(c)
Q.4
A lamp emits monochromatic green light uniformly in all directions. The lamp is 3% effecient in converting electrical power to electromagnetic waves and consumes 100W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 5m from the lamp will be
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a) 1.34 V/m
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b) 2.68 V/m
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c)4.02 V/m
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d)5.36 V/m
Explanation
Average intenisty=P / 4πR2 and Average intenisty=ε0 Eo2×c from above two equations Answer:(b)
Q.5
The Sun radiates electromagentic energy at the rate of 3.9×1026 W. Its radius is 6.96×108 m . The intensity of sun light ( in W/m2) at the solar surface will be
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a) 5.6×106
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b) 5.6×107
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c) 4.2×106
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d) 4.2×107
Explanation
USe formula Intenisty=P/A Answer: (b)
Q.6
An electromagnetic wave of frequency ν=3.0 Mhz passes from vacuum into a dielectric medium with permitivity ε=4.Then [ AIEEE 2004]
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a)Wavelength is doubled and frequency remains unchaged
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b) Wvaelength is doubled and frequency becopmes half
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c)wavelength is doubled and frequency becomes half
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d)wave length and frequency both remains unchaged
Explanation
Use formula velocity v=1 / √(εµ) and velocty v=λν ( frequency ν reamins constant)Answer: (c)
Q.7
The electrical conductive it of earth's atmosphere increases with altitude because of [ Bihar CECE 2004]
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a) reflection of atmospheres
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b) accelerated protons
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c)measure of voltagae
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d)measure of charge
Explanation
Answer: (a)
Q.8
If the wavelength of light is 4000 Å then the number of waves in 1mm length will be [ JKCET 2004]
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a) 25
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b) 0.25
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c)0.25×104
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d)2.5×104
Explanation
Answer:(c)
Q.9
Sodium lamps are used in foggy conditions because
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a) yellow light is scatered less by the fog particles
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b) yellow light is scattered more by the fog particles
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c) yellow light is unaffected during its passage through the fog
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d) wavelength of yellow light is the mean of visible part of the sprectrum
Explanation
Answer: (a)
Q.10
The rms value of electric field of the radiation coming from sun is 720 N/C, The average radiation density in J/m3 is ..
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a)81.35 × 10-12
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b) 3.3 × 10-3
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c)4.58 × 10-6
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d)6.37 × 10-9
Explanation
Energy density ρ=εoErms2 Answer: (c)
Q.11
In the region closer to the oscillating charges, the phase difference between E and B fields is ... and their magnitude quickly decreases as ... with distance r from the source
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a) 0, r-1
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b) π/2, r-3
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c)π/2, r-1
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d)0, r-3
Explanation
Answer: (b)
Q.12
At room temperature, if the relative permittivity of water be 80 and the relative permeability be 0.0222, then the velocity of light in water is ... m/s
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a)3×108
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b) 2.5×108
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c)2.25×108
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d)3.5 ×108
Explanation
Answer:(c)
Q.13
If the electric field asssociated with a radiation of frequency 10 MHz is E=10sin( kx -ωt) mV/m . then its energy density in J/m3 is [ εo=8.85×10-12C2N-1m-2]
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a) 4.425×10-16
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b) 6.26×10-14
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c) 8.85×10-16
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d) 8.85×10-14
Explanation
USe formula energy density ρ=εoErms2 and Erms=Eo / √2 Answer: (a)
Q.14
In hertz's experiment the .... of the electromagnetic waves is equal to the kinetic energy of the charges oscillating between the two spheres
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a)frequency
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b) energy
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c)wavelength
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d)velocity
Explanation
Answer: (b)
Q.15
The etensity of plane electromagnetic wave with Bo=1.0×10-4T in W/m2 is ..
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a) 2.38×106
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b) 1.19×106
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c)6×105
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d)4.76×106
Explanation
Use formula I=cBo2 / 2µoAnswer: (b)
Q.16
The magnetic field of an electromagnetic plane travelling along the negative X-direction is given by By=2×10-7 sin(0.5×103 x + 1.5×1011 t ) T what is the wavelength and frequecy of the wave
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a) 1.26 m, 23.9 Hz
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b) 2.56 cm, 12.0 GHz
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c)3.21 m , 36.2 GHz
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d)1.26 cm, 23.9 GHz
Explanation
Answer:(d)
Q.17
For a radiation of 6 GHz passing through air, the wave number ( number of waves) per 1 m length is ...(1 GhZ=109 Hz)
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a) 3
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b) 5
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c) 20
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d) 30
Explanation
use formula,number of waves=1/ λ Answer: (c)
Q.18
The power in a two-wire transmission line travels
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a)inside the conductors
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b) outside the conductors
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c)none of the above
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d)both inside and outside the conductors
Explanation
Answer: (b)
Q.19
The characteristic impedance of a lossless transmission line is given by
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a) Zo=√LC
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b) Zo=√ (L/C)
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c)Zo=√(C/L)
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d)Zo=LC
Explanation
Answer: (b)
Q.20
An 'antenna' is
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a) inductive
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b) capacittative
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c)resistive above its resonance frequency
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d)none of the above
Explanation
Answer:(a)
Q.21
A laser is a coherent source because it contains
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a) many wavelengths
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b) uncoordinated wave of a particular wavelength
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c) coordinated wave of many wavelengths
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d) coordinated waves of a particular wavelength
Explanation
Answer: (d)
Q.22
A modulating signal of frequency 5kHz and peak voltage of 6V is used to modulate a carrier of frequency 10 MHz and peak votage of 10V. what is modulation index
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a)1.66
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b) 0.6
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c)2
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d)0.5
Explanation
Modulation index ma=Em / EC=6/10=0.6Answer: (b)
Q.23
In above problem (Q161) what is Low side band frequency (LSB)
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a) 10.005 MHz
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b) 0.05 MHz
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c)22 MHz
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d)9.995 Mhz
Explanation
Frequency of LSB=fC - fm =10 -0.005=9.995 MHZAnswer: (d)
Q.24
In problem Q161 What is upper side band frequency (USB)
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a)10.005 MHz
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b)0.05 MHz
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c)22 MHz
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d)9.995 MHz
Explanation
USB=fc + fm 10.0 + 0.005=10.005 MHz Answer:(a)
Q.25
In problem Q161 what is the amplitude of LSB and USB
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a) 3V, 6V
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b) 6V, 3V
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c) 3V , 3V
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d) 6V, 6V
Explanation
Amplitude LSB=USB=maEC / 2=0.6×10 / 2=3V Answer: (c)
Q.26
Who produced the electromagnetic waves first ?
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a)Marconi
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b)Maxwell
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c)J.C. Bose
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d)Hertz
Explanation
Answer: (d)
Q.27
A plane electromagnetic wave is incident on a material surface. The wave delivers momentum P and energy E
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a) P=0, E ≠ 0
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b)P ≠ 0, E=0
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c)P ≠ 0, E ≠ 0
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d) P=0, E=0
Explanation
Answer: (c)
Q.28
If Vγ Vx and Vm are the velocity of the γ rays, x rays, micro waves respectively inspace, then
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a)Vγ < Vx < Vm
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b) Vγ=Vx=Vm
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c)Vγ > Vx > Vm
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d)Vγ > Vx < Vm
Explanation
Answer:(b)
Q.29
If λγ ,λx and λm are the wave lengths of the γ rays, x rays and micro waves respectivelyin space then
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a) λγ > λx > λm
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b) λγ < λx < λm
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c) λγ=λx=λm
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d) λγ >λm > λx
Explanation
Answer: (b)
Q.30
According to Maxwell, a changing electric field produces
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a)emf
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b) Electric current
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c)magnetic field
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d)radiation pressure
Explanation
Answer: (c)
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